src/tools/clippy/clippy_lints/src/loops/single_element_loop.rs

   1 use super::SINGLE_ELEMENT_LOOP;
   2 use clippy_utils::diagnostics::span_lint_and_sugg;
   3 use clippy_utils::source::{indent_of, snippet_with_applicability};
   4 use if_chain::if_chain;
   5 use rustc_ast::util::parser::PREC_PREFIX;
   6 use rustc_ast::Mutability;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{is_range_literal, BorrowKind, Expr, ExprKind, Pat};
   9 use rustc_lint::LateContext;
  10 use rustc_span::edition::Edition;
  11
  12 pub(super) fn check<'tcx>(
  13     cx: &LateContext<'tcx>,
  14     pat: &'tcx Pat<'_>,
  15     arg: &'tcx Expr<'_>,
  16     body: &'tcx Expr<'_>,
  17     expr: &'tcx Expr<'_>,
  18 ) {
  19     let (arg_expression, prefix) = match arg.kind {
  20         ExprKind::AddrOf(
  21             BorrowKind::Ref,
  22             Mutability::Not,
  23             Expr {
  24                 kind: ExprKind::Array([arg]),
  25                 ..
  26             },
  27         ) => (arg, "&"),
  28         ExprKind::AddrOf(
  29             BorrowKind::Ref,
  30             Mutability::Mut,
  31             Expr {
  32                 kind: ExprKind::Array([arg]),
  33                 ..
  34             },
  35         ) => (arg, "&mut "),
  36         ExprKind::MethodCall(
  37             method,
  38             Expr {
  39                 kind: ExprKind::Array([arg]),
  40                 ..
  41             },
  42             [],
  43             _,
  44         ) if method.ident.name == rustc_span::sym::iter => (arg, "&"),
  45         ExprKind::MethodCall(
  46             method,
  47             Expr {
  48                 kind: ExprKind::Array([arg]),
  49                 ..
  50             },
  51             [],
  52             _,
  53         ) if method.ident.name.as_str() == "iter_mut" => (arg, "&mut "),
  54         ExprKind::MethodCall(
  55             method,
  56             Expr {
  57                 kind: ExprKind::Array([arg]),
  58                 ..
  59             },
  60             [],
  61             _,
  62         ) if method.ident.name == rustc_span::sym::into_iter => (arg, ""),
  63         // Only check for arrays edition 2021 or later, as this case will trigger a compiler error otherwise.
  64         ExprKind::Array([arg]) if cx.tcx.sess.edition() >= Edition::Edition2021 => (arg, ""),
  65         _ => return,
  66     };
  67     if_chain! {
  68         if let ExprKind::Block(block, _) = body.kind;
  69         if !block.stmts.is_empty();
  70         then {
  71             let mut applicability = Applicability::MachineApplicable;
  72             let pat_snip = snippet_with_applicability(cx, pat.span, "..", &mut applicability);
  73             let mut arg_snip = snippet_with_applicability(cx, arg_expression.span, "..", &mut applicability);
  74             let mut block_str = snippet_with_applicability(cx, block.span, "..", &mut applicability).into_owned();
  75             block_str.remove(0);
  76             block_str.pop();
  77             let indent = " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0));
  78
  79             // Reference iterator from `&(mut) []` or `[].iter(_mut)()`.
  80             if !prefix.is_empty() && (
  81                 // Precedence of internal expression is less than or equal to precedence of `&expr`.
  82                 arg_expression.precedence().order() <= PREC_PREFIX || is_range_literal(arg_expression)
  83             ) {
  84                 arg_snip = format!("({arg_snip})").into();
  85             }
  86
  87             span_lint_and_sugg(
  88                 cx,
  89                 SINGLE_ELEMENT_LOOP,
  90                 expr.span,
  91                 "for loop over a single element",
  92                 "try",
  93                 format!("{{\n{indent}let {pat_snip} = {prefix}{arg_snip};{block_str}}}"),
  94                 applicability,
  95             )
  96         }
  97     }
  98 }